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Palaeogeographical reconstruction of successive rift lake environments in the northern and central segments of the Kenya Rift from Paleogene to middle-upper Miocene: To the search of potential source and reservoir rocks

Abstract : The present-day rift morphologies and sedimentary environments of the northern (NKR) and central (CKR) segments of the Kenya Rift are characterized: 1) in the north, from 5° to 3°N, by a single half-graben rift basin that hosts today Lake Turkana; and 2) this single half-graben evolves to the south, from about 2°30'N, toward a double, fully symmetric half-graben system with to the west, the Kerio half-graben today occupied by a single, semi-perennial fluvial system, and to the east a complex half-graben basin that hosts the shallow freshwater Lake Baringo to the north, and the saline, alkaline and organic-rich Lake Bogoria to the south. Early rifting processes in this part of the Eastern Branch of the East African Rift System started during Eocene times in the region located between 3° and 2°30'N, and resulted in the development of a set of two parallel, N-S oriented half-graben basins - the Lokichar Basin to the west; the North Kerio Basin to the east - similar to the set of present-day Kerio and Baringo-Bogoria Basins. Vertical movements along the major border faults in the NKR resulted in two long-lived lacustrine environments, Lake Lokichar to the west, and the North Kerio Lake to the east. These lakes developed from Eocene under tropical climatic conditions and no volcanic activity in the region. This induced the deposition of thick high TOC shales alternating with wide fluvio-deltaic bodies that extended into the basins during periods of lake regression. Transgressive periods resulted in a single large lake occupying both the Lokichar and North Kerio Basins. Finally, these basins ended at around middle Miocene, consequently to a major change in climate and occurrence of intense volcanic activity in the area. During the Eocene period in the CKR, sedimentation of unknown type developed into the precursors of the Kerio and Baringo-Bogoria Basins. The presence at depth of sedimentary deposits is only demonstrated by geophysical data obtained in the Kerio and Baringo Basins, and by the Kimwarer and Kamego Formations, both poorly exposed in the Kerio and Baringo Basins and which are possible relicts of these early rift deposits. These basement-sourced sediments are mainly of alluvial fan and fluvial type, with brief occurrences of shallow lake environment. At the contrary of the southern NKR, abundant volcanism marked by large volumes of basaltic/phonolitic lavas resulted in the complete filling by lavas of the whole central segment from 23 to 15 Ma. Later on, major vertical movements along the Elgeyo, Saimo and Laikipia border faults contributed to create two new half-grabens prefiguring the present-day Kerio and Baringo Basins. From early to middle Miocene, large lake bodies developed in these two basins, where they are illustrated by the Tambach and Ngorora Formations both representative of large freshwater to saline lake environments with good source rocks potential. From about 8 Ma, rifting migrates from west to east, resulting in a single tectonically active half-graben that hosted a suite of lacustrine environments of which present-day Lakes Baringo and Bogoria are the remnants.
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Submitted on : Wednesday, February 26, 2014 - 1:18:01 PM
Last modification on : Friday, April 5, 2019 - 8:17:35 PM

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George Muia, Jean-Jacques Tiercelin. Palaeogeographical reconstruction of successive rift lake environments in the northern and central segments of the Kenya Rift from Paleogene to middle-upper Miocene: To the search of potential source and reservoir rocks. 6th East African Petroleum Conference, Feb 2013, Arusha, Tanzania. ⟨insu-00952197⟩

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